1. Field
The present disclosure relates generally to wireless communication devices and, more specifically, to a method of monitoring paging channels to extend standby time.
2. Background
Mobile subscribers consider long battery life to be a positive attribute of a cell phone. Battery life is typically described in terms of talk time and standby time. Even when a mobile subscriber is not carrying on a conversation, his cell phone still consumes power. Standby time is the length of time a battery can power a cell phone even when no calls are made. Under the IS-95 standard promulgated by the Telecommunications Industry Association/Electronic Industry Association relating to code division multiple accessing (CDMA), when a cell phone is turned on, the cell phone first acquires a pilot channel, a synchronization channel and a paging channel before transmitting and receiving voice traffic over a traffic channel. Once the paging channel is acquired, power is conserved by shutting down certain circuitry in the cell phone until a call is received or made. Other circuitry, however, must nevertheless be powered to detect whether the cell phone is receiving a call. In the slotted paging mode of the IS-95 standard, certain circuitry is turned on periodically to monitor a general paging message in the paging channel. If the general paging message does not contain a page, the circuitry is turned off again.
Even periodically monitoring the general paging message, however, consumes power. Standby time can be further extended by using a quick paging channel (QPCH), which was introduced by the CDMA IS-2000 standard. The paging channel and the quick paging channel are distinct code channels. The quick paging channel includes quick paging bits (also called paging indicator or PI bits) that are set to indicate a page in the general paging message of the paging channel. If both quick paging bits in the quick paging channel are not set, the mobile station need not demodulate the subsequent general paging message in the general paging channel. Less energy is consumed demodulating the quick paging bits than demodulating the relatively longer general paging message. By demodulating the quick paging bits of the quick paging channel, the general paging message in the paging channel can be demodulated only when there is a page.
Under certain conditions, however, using the quick paging channel to indicate a page can consume more power than monitoring the paging channel alone. The quick paging bits are modulated with on-off keying (OOK), and demodulating a quick paging bit in a high noise environment can incorrectly indicate that the quick paging bit has been set. As the noise level rises, demodulating the quick paging bits results in a higher percentage of false alarms from incorrectly reading quick paging bits. At some noise threshold, the power required to demodulate the quick paging bits as well as the general paging message after a false alarm is greater than the power required to demodulate only the general paging message. Consequently, standby time can actually decrease when the quick paging channel is used in high noise environments.
Standby time increases when the quick paging mode can be used without increasing the percentage of false alarms. Thus, a method is sought for extending standby time by increasing the noise level at which a cell phone can operate in the quick paging mode without generating excessive false alarms.